BIOLOGICAL
MOLECULES OF LIFE
CARBOHYDRATES, LIPIDS, PROTEINS, AND NUCLEIC ACIDS
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Carbon

Carbon is a central element to life because most biological
molecules are built on a carbon framework.

The complexity of living things is facilitated by carbon’s linkage
capacity.

Carbon has great bonding capacity due to its tetrahedral structure.

Carbon’s outer shell has only four of the eight electrons necessary
for maximum stability in most elements.

Carbon atoms are thus able to form stable, covalent bonds with a
wide variety of atoms, including other carbon atoms.
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Organic vs Inorganic Compounds


Compounds which contain carbon – carbon bonds are called
organic molecules.
•
Contain carbon and hydrogen.
•
Contains single, double, or triple covalent bonds.
•
Examples – methane, ethane, sugar, lipids
Compounds which do not contain carbon – carbon bonds are
called inorganic.
•
Examples – water, oxygen, ammonia, salt
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Organic Compounds
•
always contain carbon and hydrogen, and sometimes
oxygen, sulfur, nitrogen, phosphorus, or a halogen
•
occur in nature and are also found in fuel, shampoos,
cosmetics, perfumes, and foods
•
are the foundation for understanding biochemistry
•
have low melting and boiling points
•
are not soluble in water and are less dense
than water
•
undergo combustion, burning vigorously in air
Formulas for organic compounds are written with carbon
first, followed by hydrogen and then other elements.
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Organic vs Inorganic Compounds
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Hydrocarbons
Hydrocarbons are organic compounds that
contain only carbon and hydrogen.
Saturated hydrocarbons contain only single
carbon-carbon bonds.
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Molecules of Life
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Monomers and Polymers
Biological molecules are made by monomers
bonding to form polymers
Monomers
•
Molecules that are building blocks for larger molecules
•
Simple sugars, fatty acids, amino acids, nucleotides
Polymers
•
Molecules that consist of multiple monomers
•
Carbohydrates, lipids, proteins, nucleic acids
•
Polymers are made by dehydration synthesis
(removal of water)
•
Polymers are broken apart by hydrolysis
(addition of water).
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Monomers and Polymers
Dehydration of Synthesis
Hydrolysis
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Carbohydrates
• Carbohydrates are formed from the building blocks
or monomers of simple sugars, such as glucose.
• Some simple sugars have the same chemical
formula but are arranged differently, such as glucose
and fructose. These are called isomers.
• These monomers can be linked to form larger
polymers, which are known as disaccharides
polysaccharides (complex carbohydrates).
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Carbohydrates - Disaccharides
Disaccharides are two simple sugars bonded
together.
Some examples include:

Sucrose = glucose + fructose
•

Lactose = glucose + galactose
•

Table sugar
Milk sugar
Maltose = glucose + glucose
•
Found in germinating grains, malt products
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Carbohydrates - Polysaccharides
Polysaccharides are made up of many monomers joined
together.
Four polysaccharides are critical in the living world:
 Starch
•

Glycogen
•

nutrient storage form of carbohydrates in animals
Cellulose
•

nutrient storage form of carbohydrates in plants
rigid, structural carbohydrate found in the cell walls of many
organisms
Chitin
•
tough carbohydrate that forms external skeleton of arthropods.
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Carbohydrates - Polysaccharides
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Lipids
The defining characteristic of all lipids is that they do
not readily dissolve in water.
 Lipids do not possess the monomers-to-polymers
structure seen in other biological molecules; no one
structural element is common to all lipids.
 Lipids include


•
Triglycerides
•
Steroids
•
Phospholipids
•
Waxes
Lipids are used for
•
Storing energy
•
Insulating and cushioning
•
Hormones - steroids
•
Waterproofing
•
Cell membranes
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Lipids - triglycerides

Among the most important lipids are the triglycerides,
composed of a glyceride and three fatty acids.

Most of the fats that human beings consume are triglycerides.

Saturated fats are triglyceride molecules that have only single
bonds.

Unsaturated fats are triglyceride molecules that have at least
one double bond. The two types of unsaturated fats are:

•
Cis fat – naturally occurring configuration of double bond
•
Trans fat – artificially created configuration of double
Hydrogenated fats are artificially created saturated fats made
from cis fats.
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Lipids – steroids


Another important variety of lipids is the steroids, all of
which have a core of four carbon rings with various
functional groups attached.
Examples include cholesterol and such hormones as
testosterone and estrogen.
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Lipids – phospholipids

A third class of lipids is the phospholipids, each of which is
composed of two fatty acids, glycerol, and a phosphate group.

The phosphate end is polar and attracts water. The fatty acid end
is nonpolar and repels water.

The material forming the outer membrane of cells is largely
composed of phospholipids.
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Lipids – waxes

A fourth class of lipids is the waxes, each of which is composed of a
single fatty acid linked to a long-chain alcohol.

Waxes have an important “sealing” function in the living world.

Almost all plant surfaces exposed to air, for example, have a
protective covering made largely of wax.
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Proteins

Proteins are an extremely diverse group of biological
molecules composed of the monomers called amino
acids.

Sequences of amino acids are strung together to produce
polypeptide chains, which then fold up into working
proteins.

Important groups of proteins include enzymes, which
hasten chemical reactions, and structural proteins,
which make up such structures as hair.
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Types of Proteins
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Proteins – Amino acids
Amino acids:
•
are the building blocks of proteins.
•
contain a carboxylic acid group and an amino group on the alpha ()
carbon.
•
contain a side chain of atoms (R)
•
are ionized in solution.
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Proteins – Amino acids
There are 20 common amino acids found in human
proteins.
The 20 amino acids are classified into four categories
based on their side chains (R- groups)
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Proteins – The 20 Amino acids
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Proteins – The Beginning of a Protein
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Proteins – Hierarchy of Protein Structure
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Lipoproteins & Glycoproteins
Lipoproteins

Lipoproteins are biological molecules that are
combinations of lipids and proteins.

High-density and low-density lipoproteins (HDLs and
LDLs, respectively), which transport cholesterol in
human beings, are important determinants of human
heart disease.
Glycoproteins

Glycoproteins are combinations of carbohydrates and
proteins.

The signal-receiving receptors found on cell surfaces
often are glycoproteins.
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Nucleic Acids
Nucleic acids are polymers composed of nucleotides.
The nucleic acids are composed of nucleotides that
contain a sugar, a phosphate group, and one of five
nitrogen-containing bases.
There are two types of nucleic acids


DNA, deoxyribonucleic acid
•
DNA is the repository of genetic information
•
The sequences of bases in DNA encodes the information
necessary for production of proteins in living things.
RNA, ribonucleic acid
•
RNA transports the information in encoded in DNA to the sites of
protein synthesis.
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Nucleic Acids - Nucleotides
Nucleotides consist of:

A pentose sugar
•
Deoxyribose for DNA
•
Ribose for RNA

A phosphate group

A nitrogenous base either a pyrimidine or a purine
The pyrimidines include:
•
Cytosine (C) and Thymine (T) for DNA
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Cytosine (C) and Uracil (U) for RNA
The purines include:
•
Adenine (A) and Guanine (G)
When Nucleic Acids hydrogen bond to each other they always pair up C
to G, and A to T in DNA. For RNA , they pair up C to G and A to U.
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Questions
Prepared and Compiled from various sources by
D. Leonard (Learning Specialist)
The Academic Support Center @ Daytona State College
http://www.daytonastate.edu/asc/ascsciencehandouts.html
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